1. Field of the Invention
This invention relates to a piston of refractory materials, used in an internal combustion engine and more particularly in a compression-ignition engine.
2. Description of the Prior Art
In the design of compression-ignition engines, it has been proposed to use insulated combustion chambers to increase efficiency and reduce pollution. Moreover, the available heat to drive the turbine of a turbocharged engine is thereby considerably increased. A known solution consists of spraying a ceramic-base insulating material on the surfaces of the combustion chamber.
Another common solution is to form at least one of the components that define the combustion chamber of an insulating material. As a variant, a ceramic insert can be embedded in one of these components or a thermal shield can be added.
In the first solution, difficulties arise in maintaining the integrity of the insulating layer because of the stresses due to the combustion cycle and consequently because of the problems of thermal expansion.
With these solutions, difficulties also arise which are caused by the considerable temperature gradients existing between the materials. Excessive thermal stresses and deformations can result when a material which does not have an extremely low coefficient of thermal expansion is involved.